Various suggestions have been made for improving the properties of chemical and chemical/mechanical wood pulps; for example, post-treatment of pulps with sulfur dioxide, bisulfite and neutral sulfite solutions is described in the following references: Kvisgaard, H. J. Norsk Skogind 5:155-163 (1965); Vinje, M. G., and Worster, H. E., Canadian Pat. No. 864,412, Feb. 23, 1971; Worster, H. E., Pulp and Paper Mag., Can., 75 (10): 45-50 (Oct. 1974); Kringstad, K. P., and Olausson, J., Svensk Papperstidning, 480-485 (Nov. 13, 1974); Worster, H. E., and Pudek, M. F., TAPPI 58, 11 (Nov. 1975). Such post-treatment processes have been suggested where the treatment was carried out at temperatures below the boiling point of the solution, as well as where the treatment was carried out at temperatures thereabove. However, so far as is known, all previously suggested treating processes for pulp have involved purification or control steps which were sufficiently expensive to make the processes unattractive for commercial use. For example, the indicated Kringstad and Olausson reference suggests that sodium sulfite can be used for the post-treatment of pulp slurries, but only at a pH not higher than approximately 9. When sodium sulfite is added in the proportions suggested to a pulp slurry from a commercial kraft cook the pH of the resulting slurry is normally higher than the upper limit at which sodium sulfite is claimed to be effective to improve the properties of paper made from the pulp. Accordingly, an expensive downward pH adjustment would be necessary, for example by addition of sulfuric acid.